We propose to expand upon a national survey of the interpretations given to mammograms. The previous study considered the interpretation of screening mammograms. The proposed study will examine the diagnostic interpretation of mammograms. As in the previous study, the proposed study will precisely estimate determinants of the variability in, and the accuracy of, radiologists' diagnostic interpretation of mammograms. The proposed study is a natural and logical extension of the screening study. Based on the study results, and with the participation of a distinguished national advisory panel, we will attempt to develop recommendations for potential public health interventions and intervention targets to improve the effectiveness of diagnostic mammogram interpretation. The study will use mammography films randomly sampled from a typical screening program with disease status determined before sampling by biopsy or long-term follow-up. Some of these films were read in the survey of screening mammogram interpretation. The films and additional work-up will be interpreted by the same radiologists who participated in the survey of screening interpretation. These radiologists had been randomly sampled from facilities accredited by the FDA as of January 1998. Regression models for ROC curves will be used to relate variability in interpretation and diagnostic accuracy as functions of radiologist and case characteristics. Using the paired data from both surveys, we will test whether skill in screening mammogram interpretation equates to skill in diagnostic mammogram interpretation. We will also estimate the improvement in accuracy that is generated by additional work-up. Our sampling design and statistical methods will minimize and control for possible biases coming from self-selection by radiologists.